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It stores each database (composed of tables, indices, etc.) in a single file. Since a
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It stores each database (composed of tables, indices, etc.) in a single file. Since a
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single SDF occupies a whole database, each SDF will be contained in a single file.
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single SDF occupies a whole database, each SDF will be contained in a single file.
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Each SDF file contains the following tables:
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Each SDF file contains the following tables:
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\itemize{
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\itemize{
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\item{sdf_attributes}{a key-value table that contains the SDF attributes. Currently,
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\item{sdf\_attributes}{a key-value table that contains the SDF attributes. Currently,
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only \emph{name} is used representing the SDF's internal name.}
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only \emph{name} is used representing the SDF's internal name.}
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\item{sdf_data}{contains the actual data. Factors and ordered variables are stored as
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\item{sdf\_data}{contains the actual data. Factors and ordered variables are stored as
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integers. Their levels are stored in other tables. Numeric (real) are stored as double,
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integers. Their levels are stored in other tables. Numeric (real) are stored as double,
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characters as text and integers as int's. Currently, complex numbers are not supported.
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characters as text and integers as int's. Currently, complex numbers are not supported.
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Column names correspond exactly to the variable names of the ordinary data frames. E.g.
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Column names correspond exactly to the variable names of the ordinary data frames. E.g.
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Petal.Length will have a column name Petal.Length in the table. This is possible
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Petal.Length will have a column name Petal.Length in the table. This is possible
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because SQLite allows almost any kind of column name as long as it is quoted by
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because SQLite allows almost any kind of column name as long as it is quoted by
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    iris.sdf$Petal.Length[1:10]
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    iris.sdf$Petal.Length[1:10]
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    iris.sdf[["Petal.Length"]][1:10]
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    iris.sdf[["Petal.Length"]][1:10]
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    iris.sdf[1,c(TRUE,FALSE)]
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    iris.sdf[1,c(TRUE,FALSE)]
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    #apply(iris.sdf[1:4], 2, mean)
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    #apply(iris.sdf[1:4], 2, mean)
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}
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}
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\keyword{data}
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\keyword{manip}
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\keyword{classes}